0702 - common disturbances of cardiac rhythm - AHF Flashcards
What is the difference between a narrow and broad complex tachycardia?
Narrow: narrow QRS complex (< 0.12 s, < 3 small squares)
Broad: broad QRS complex (> 0.12 s, > 3 small squares)
Define sinus rhythm.
Normal rate (60 - 100 bpm) and rhythm (PR interval consistent).
Define sinus bradycardia.
- bradycardiac rate (<60 bpm) and normal rhythm
- common in individuals during sleep and in those with high vagal tone (i.e. athletes, young healthy adults)
- may be pathological (e.g. AMI, drugs, sick sinus syndrome, hypothermia)
Define sick sinus syndrome.
A form of bradycardia; due to SA node dysfunction; 2 main types:
- sinoatrial block
- transient failure of impulse conduction to atrial myocardium
- intermittent pauses between P waves
- sinus arrest
- transient cessation of impulse formation at SA node
- prolonged pause without P wave activity
Outline some conditions associated with SA node dysfunction.
- age
- idiopathic fibrosis
- ischaemia (including MI)
- high vagal tone
- myocarditis
- digoxin toxicity
Define atrioventricular (AV) block.
Atrial depolarisations fail to reach the ventricles, or when atrial depolarisation is conducted with a delay; 3 degrees of AV block recognised:
- first degree AV block
- PR interval consistently >0.2 s
- but atrial impulses do reach ventricles, just delayed
- does not require treatment
- second degree AV block
- type I (Wenckebach) (
PR interval gets longer and longer;
does not require treatment)
- type II (
constant PR interval followed by dropped P wave;
not every P wave associated with a QRS complex;
requires treatment as more likely to lead to a third degree block)
- third degree AV block
- multiple P waves not conducting all the time, when does, PR interval constant
- no association between P wave and QRS complex (both are regular, but no relationship between the two)
- requires treatment
How are tachycardias broadly classified?
- Supraventricular tachycardia:
a. Stemming from atria, or SA node
i. Sinus tachycardia
ii. Atrial fibrillation
iii. Atrial flutter
iv. Atrial tachycardia
b. Stemming from AV node
i. Atrioventricular re-entrant tachycardia
ii. Atrioventricular nodal re-entrant tachycardia
c. Bundle branch block with aberrant conduction (broad complex)
d. Atrial tachycardia with pre-excitation (broad complex) - Ventricular tachycardia:
a. Regular rhythm (monomorphic - QRS complexes have same general appearance)
i. Monomorphic
ii. Fascicular
iii. Right ventricular outflow tract
b. Irregular rhythm (polymorphic - QRS complexes vary in morphology)
i. Torsades de pointes
ii. Polymorphic
Describe sinus tachycardia.
- normal P wave
- every P wave associated with a QRS complex
- regular, but faster rate
- physiological (exertion, anxiety, pain), pathological (fever, anaemia, hypovolaemia, hypoxia), endocrine (thyrotoxicosis) and pharmacological causes (adrenaline, salbutamol, alcohol, caffeine)
Describe atrial fibrillation (AF).
- result of multiple wavelets of depolarisation moving around the artia chaotically
- P waves absent
- fine baseline oscillations
- irregular ventricular complexes
- QRS complexes irregularly irregular
- ventricular rate (and hence HR) depends on degree of AV node conduction
- most common sustained arrhythmia
- causes include ischaemic heart disease, hypertensive heart disease, rheumatic heart disease, cardiomyopathy, alcohol misuse, sick sinus syndrome, chronic pulmonary disease, idiopathic
- prognosis excellent when AF due to idiopathic causes
- prognosis poor when due to ischaemic cardiomyopathy
Describe atrial flutter.
- due to a re-entry circuit in RA, with secondary activation of LA
- fast atrial contractions
- saw-toothed flutter waves on ECG
- may convert into atrial fibrillation
- causes similar to atrial fibrillation, except idiopathic atrial flutter uncommon
Describe atrial tachycardia.
- typically arises from ectopic source in atrial muscle
- P waves can be abnormally shaped
- types:
- benign
i. abrupt onset and cessation
ii. brief in duration - incessant ectopic
- multifocal
i. multiple sites in atria discharging due to increased automaticity
ii. P wave morphology varies
iii. PR intervals different lengths
iv. typically seen in association with chronic pulmonary disease
* atrial tachycardia with block
Define supraventricular tachycardia.
- aka junctional tachycardia
- arises from atrioventricular junction as a result of re-entry mechanism
- initiated by a premature ventricular contraction
- types:
- atrioventricular nodal re-entrant
i. most common supraventricular tachycardia
ii. ectopic beat conducted in AV node through slow pathway (lower conduction velocity, shorter refractory period) because fast pathway still in refractory period, once depolarisation wave through slow pathway, fast pathway read to be depolarised so wave moves through it and hence retrogradally, establishing a circuit (in sinus rhythm, atrial impulse conducted through fast pathway and depolarises the ventricles)
iii. inverted P wave - atrioventricular re-entrant
i. occurs due to conduction moving through a different pathway to the ventricles from the atria, instead of through the AV node; “accessory conduction pathway”, leading to premature activation of ventricles and formation of a re-entry circuit
ii. e.g. Wolff-Parkinson-White syndrome
Describe torsades de pointes tachycardia.
- cardiac axis rotates over a sequence of 5 - 20 beats
- QRS complex amplitude varies
- associated with conditions that prolong the QT interval
- has a different management to other ventricular tachycardias
In the clinical setting, how can we differentiate between ventricular tachycardia (VT) and supraventricular tachycardia (SVT) with bundle branch block?
- VT: no association between P waves and QRS complexes; QRS complexes > 0.14 s
- SVT: P waves associated with QRS complexes
- a broad complex tachycardia in patients > 35 years old more likely to be VT
- Px with history of ischaemic heart disease or congestive cardiac failure more likely to be VT
- safest option with a broad complex tachycardia of uncertain origin is to treat it as VT unless good evidence suggests SVT
